Optimer Files New Drug Submission for DIFICID™ in Canada, Creates Canadian Subsidiary to Lead Commercial Effort

SAN DIEGO and TORONTO, Nov. 3, 2011 /PRNewswire/ -- Optimer Pharmaceuticals, Inc. (NASDAQ: OPTR) announced today that the Company filed a new drug submission (NDS) with the Therapeutic Products Directorate of Health Canada (Health Canada) for DIFICID™ (fidaxomicin) tablets for the treatment of Clostridium difficile infection (CDI),also known as Clostridium difficile-associated diarrhea (CDAD). Health Canada awarded Optimer priority review of the DIFICID NDS, reducing the time to a potential regulatory approval in Canada. To address the country-specific needs and relationships, Optimer also announced the establishment of Optimer Pharmaceuticals Canada, Inc., a subsidiary from which the Company plans to make DIFICID available in Canada.

"C. difficile has been a major problem in Canada as evidenced by recent outbreaks, and we believe there is a significant need there for new CDI treatment options," said Pedro Lichtinger, President and CEO of Optimer Pharmaceuticals. "Canada represents our first direct entry into an international market, supporting wider DIFICID access to patients in need and advancing the treatment of hospital acquired infections."

Optimer has appointed Paulash Mohsen as country manager for Optimer Canada. Mr. Mohsen has been serving as Vice President of Strategy and Business Operations for Optimer. Before joining Optimer he spent over a decade at Pfizer where he most recently held the position of Vice President of Multi-Channel Management. Previously Mr. Mohsen was a consultant at McKinsey & Co, serving clients across the pharmaceutical industry. Mr. Mohsen holds a BS in chemical engineering from Brown University, an MS in engineering from the Massachusetts Institute of Technology and an MBA from the Harvard Business School.

"The problems presented by C. difficile infection and the need for new therapies for patients are widely understood in Canada, and there is also significant physician interest in DIFICID based on experience and familiarity gained there during the clinical development program, in which we enrolled over 400 Canadian CDI patients," noted Mr. Mohsen. "With these understandings, we conducted a thorough analysis of the most efficient way to facilitate patient access to DIFICID in the Canadian market and determined that a direct effort leveraging regional experience from our clinical program and manufacturing logistics is the best means to do so."

The NDS is based on the results of two Phase 3 clinical studies of DIFICID in patients with CDI. The trials were multi-center, randomized, double-blind trials, which enrolled a total of 1,164 adult subjects. Subjects with confirmed CDI received either DIFICID (200 mg twice daily) or oral vancomycin (125 mg four times daily). The primary objective of both studies was to show that a 10-day course of DIFICID was as effective as oral vancomycin in achieving a clinical response, defined as patients requiring no further CDI therapy two days after completion of study medication, at the end of therapy. An additional efficacy endpoint was sustained clinical response, defined as clinical response at the end of treatment and survival without proven or suspected CDI recurrence through 30 days beyond the end of treatment. In both of these studies, DIFICID achieved its primary endpoint of non-inferiority compared to vancomycin. DIFICID was also statistically superior to vancomycin in sustained clinical response and reduced CDI recurrences by 47%. The most common treatment related adverse reactions in these studies were vomiting (1.2%), nausea (2.7%) and constipation (1.2%).

Optimer's Canadian subsidiary plans to hire approximately 25 employees in general and administrative, commercial, and medical affairs positions.

About CDAD

Clostridium difficile-associated diarrhea (CDAD) has become a significant medical problem in hospitals, long-term care facilities and in the community. CDAD is a serious illness resulting from infection of the inner lining of the colon byC. difficile bacteria, which produce toxins that cause inflammation of the colon, severe diarrhea and, in the most serious cases, death. Patients typically develop CDAD from the use of broad-spectrum antibiotics that disrupt normal gastrointestinal (gut) flora, possibly allowing C. difficile bacteria to flourish. Older patients in particular are at risk for CDAD, potentially because of a weakened immune system or the presence of underlying disease. Approximately two-thirds of CDAD patients are 65 years of age or older. Historically, approximately 20% to 30% of CDAD patients who initially respond to treatment experience a clinical recurrence.

About Optimer

Optimer Pharmaceuticals, Inc. is a biopharmaceutical company focused on discovering, developing and commercializing innovative hospital specialty products that have a positive impact on society. In the United States, Optimer has developed and commercialized DIFICID™ (fidaxomicin) tablets, an FDA-approved antibacterial drug for the treatment of adult patients with Clostridium difficile-associated diarrhea (CDAD). Optimer has filed a marketing authorization application with the European Medicines Agency and a new drug submission with Therapeutic Products Directorate of Health Canada for fidaxomicin. Additional information can be found at http://www.optimerpharma.com.

Forward Looking Statements

Statements included in this press release that are not a description of historical facts are forward-looking statements, including without limitation statements related to the potential approval and commercialization of DIFICID in Canada, Optimer's hiring plans in Canada, Optimer's plans to market and sell DIFICID in Canada, if approved, and the potential demand for DIFICID among Canadian physicians. Words such as "believes", "would", "anticipates", "plans", "expects", "may", "intend", "will", and similar expressions are intended to identify forward-looking statements. The inclusion of forward-looking statements should not be regarded as a representation by Optimer that any of its plans will be achieved. These forward-looking statements are based on management's expectations on the date of this release. Actual results may differ materially from those set forth in this release due to the risks and uncertainties inherent in Optimer's business including, without limitation, risks relating to: whether or when DIFICID will be approved for commercial sale in Canada, Optimer's ability to successfully establish Optimer Canada and commercialize DIFICID in Canada, if approved, Optimer's ability to recruit and train a sales force and other personnel in Canada and manage the complexities involved in international operations, whether healthcare professionals will prescribe DIFICID, whether DIFICID will receive reimbursement coverage from healthcare payers and government agencies, the extent to which DIFICID will be accepted on hospital formularies, the possibility of alternative means of preventing or treating CDAD impacting adoption and sales of DIFICID in Canada, and other risks detailed in Optimer's filings with the Securities and Exchange Commission. Forward-looking statements speak only as of the date of this release, and Optimer undertakes no obligation to update or revise these statements, except as may be required by law.